NASA's Van Allen Probes have been exploring the hostile radiation belts surrounding Earth for just three months. But already, they've collected detailed measurements of high-energy particles and radio waves.

Scientists say these waves can provide an energy boost to radiation belt particles, somewhat like ocean waves can propel a surfer on Earth. What's more, these so-called chorus waves operate in the same frequency as human hearing so they can be heard.

A University of Iowa physicist played a recording of these high-pitched radio waves at a conference Tuesday in San Francisco. Craig Kletzing says it sounds like the chirping of "alien birds" and crickets.